This invention concerns the processing of carbonaceous materials. More particularly, it concerns the conversion of coal into by-products. It further concerns the conversion of caking coal into liquid products. A particular utility of the invention resides in its use in the hydropyrolysis of caking coal to produce desirable liquid products.
In many processes involving the heating of coal, such as hydropyrolysis, a problem frequently encountered concerns the tendency of coal to melt or become plastic over a range of temperature, depending on the type of coal involved. In this temperature range, coal becomes sticky and tends to adhere to various portions of the reactor, such as walls, inlet tubes, etc. In the case of pulverized coal, at this particular temperature range, the particles tend to exhibit a "popcorn effect," at which time the particles swell and lose volatile material. Consequently, each particle has an increase in volume, a loss in density, and a loss in weight. When contacting each other, in the "wet" stage, these particles tend to cluster and agglomerate, adhering due to one or more of the materials being volatilized. Depending on a number of factors, such as the temperature, type of coal, particle velocity, container diameter, etc., sufficient agglomeration may occur to result in plugging of the reactor. In the coal industry, the terms "agglomerating" and "caking" are frequently used interchangeably. We recognize both of these terms, but we prefer "agglomerating" and "nonagglomerating" to separate the types of coal involved. As mentioned above, agglomeration appears to be a gradual phenomenon, depending on the circumstances and conditions.
Several patents exist which show how pulverized agglomerating coal can be injected into a hot reactor. For example, in U.S. Pat. No. 4,200,494, fresh coal particles are introduced into a hot fluidized bed at velocities in excess of 200 ft/sec. The high velocity at which the particles are injected prevents agglomeration because the particles' momentum overcomes the cohesive forces of the sticky material they secrete. The turbulence of the jet forces the sticky particles into "dry" regions of the fluidized bed where the wet particles lose their stickiness.
In U.S. Pat. No. 4,206,032, agglomerating coal is injected into a hot empty reactor as a highly turbulent jet of hot hydrogen gas and coal. Mixing is rapid, such as in a rocket engine. This prevents coal from agglomerating, because the mechanical action of the gas prevents the coal particles from adhering to one another.